Luigi's Mansion 2 is one of the 3DS' best exclusives (one of many, I should point out), and if you're looking for a saving, Tesco Direct's TDX-KPWM voucher code does the business. Since first-party 3DS titles tend to hold their value longer than most, I wouldn't expect prices to fall much lower than £25 for a while - though I'd be happy to be proven wrong.